Steel manufacture



Patented Dec. 2, 1952 STEEL MANUFACTURE Jean Charles Fourmanoit, Brussels, Belgium No Drawing.

Application June 29, 1951, Serial No. 234,451. In Great Britain January 13, 1949 6 Claims.

This invention relates to steel manufacture; and it relates to a process of making steel which is particularly applicable to the acid open hearth process wherein a steel furnace is charged with metallic steel making ingredients and wherein at least a substantial part of the carburizing and deoxidizing components in the charge consists of blooms of sponge iron substantially uniformly impregnated throughout with from about to 20 per cent of free carbon, followed by converting the charge in the furnace to steel in the presence of an acid slag; said blooms of sponge iron having been impregnated by immersion in an excess of a liquid hydrocarbon containing free carbon dispersed therein and of sufiicient fluidity and at a temperature ranging from about room temperature to 350 C. suflicient to cause the carbon to permeate the pores of the sponge iron blooms to their deepest regions, followed by draining on the excess hydrocarbon to obtain a product having the structure of the original sponge iron blooms with free carbon substantially uniformly distributed throughout their pores in a highly dispersed state; all as more fully hereinafter set forth and as claimed.

This application is a continuation-in-part of my copending application, Serial No. 72,742, filed January 25, 1949, now abandoned. In the parent application my process is described in general terms whereas in the present application the description is amplified and further illustrated with specific examples.

In a copending patent application, Serial No. 162,817, now Patent No. 2,558,613, I have described a method which is applicable to the basic open hearth process of making steel and in which the usual carburizing components of the steelmaking batch are replaced by fragments of lime uniformly impregnated with bituminous materials. This method is, of course applicable only to the basic open hearth process.

I have now discovered a, process by means of which the conventional carburizing components employed in acid steel making processes can be replaced and which simultaneously opens up a new and highly practical field of use for sponge iron. The latter can be produced at low cost by well known rotary kiln processes in which iron ore and carburizing agents are charged into and passed through a rotary kiln to produce sponge iron. The sponge iron can be separated from the slag magnetically. Part of the iron is in the form of blooms which may range in size up to 3 or 4 inches in diameter while part is in the form of fines. Sponge iron produced by this method is highly pure but owing to the dilllculties involved in melting down the blooms the production of sponge iron has been on a very small scale except during war time. The present invention provides a practical Way of utilizing sponge iron in the making of steel and at the same time it eliminates the necessity of using pig iron or other carburizing agents in the acid steel making processes.

I have discovered that the sponge iron blooms obtained in the usual process are sufficiently porous so that they can be impregnated with carbon in much the same fashion as the lime fragments used in my acknowledged copending application Serial No. 72,742. Surprisingly from 10 to 20 per cent of carbon can be incorporated in the blooms by treating them for from about 2 to 5 hours with a liquid of hydrocarbon containing free carbon dispersed therein, provided that the hydrocarbon dispersion is sufficiently fluid to penetrate the pores of the sponge iron. A impregnating agents I prefer bituminous material such as asphalt, coal tar, wood tar or free-carbon-containing residual distillation products of coal or petroleum, such as coal or petroleum pitch.

If it is desired to conduct the impregnating operation at room temperatures these products can be dispersed or dissolved in hydrocarbon solvents such as gasoline or kerosene but it is usually more advantageous to impregnate the sponge iron at temperatures above the melting point of the bituminous material. Any hydrocarbon material which contains free carbon in suspension therein and which can be liquefied at temperatures below about 350 C. can be used in my process.

Impregnating temperatures much above 350 C. are not advantageous since at these higher temperatures the carbon reacts with the iron to form carbides and, if exposed to the air, considerable loss of carbon occurs due to burning. The maximum carbon content obtainable by chemical reaction i. e. in cast or pig iron is about 4 per cent by weight. My sponge iron product contains several times as much available carbon in highly active form.

In order to obtain the most thorough impregnation it is desirable to employ a difierential pressure during the impregnation. For example, the sponge iron blooms can be placed in an autoclave and the air exhausted before the liquid bituminous material is introduced or the autoclave can be closed and then heated in which case the pressure which builds up inside the autoclave will assist in the penetration, or both of these expedients can be used. But it is possible to produce adequate impregnation merely by heating a vat of bituminous material over an open flame and immersing therein a wire basket containing the sponge iron blooms. Heating may be continued for a period of from about 3 to 5 hours followed by lifting the wire basket of impregnated sponge iron blooms and draining off the excess bituminous material. Any other method of impregnation can be employed which is capable of introducing from about to per cent of free carbon in the pores of the sponge iron.

The blooms of sponge iron to be impregnated are advantageously from about to 80 mm. in diameter. It is somewhat difiicult to drain off the excess bituminous material from particles which are less than about 30 mm. in diameter but of course finer particles down to about 2 mm. can be used provided that a screen is employed to separate the impregnated blooms from the excess impregnating material.

One particular advantage of my process is that the carbon in the sponge iron pores is released to the charge in the steel furnace very slowly. In fact it is not until the sponge iron melts that its carbon content is fully released and by that time carburization has occurred. t acts much like a high-carbon pig iron with respect to the supplying of carbon to the charge. This is in marked contrast to briquets of fine particles made with a bituminous binder. These disintegrate as soon as the bitumen melts and the latter then quickly burns. The carbon is thus dissipated at the very start of the process.

If my impregnated sponge iron blooms are broken or cut to examine them in section it will be found that they retain the structure of the original sponge iron. This resembles the structure of lava or of a calcareous tufia very closely.

Of course my new carburizing agent can be employed in any of the acid steel making processes to supply the desired carbon content to the steel. For example in the crucible steel process the impregnated sponge iron can be used to replace the conventional pig iron. And, of course; it is equally possible to employ the impregnated sponge iron as the carburizing component in the electric furnace steel making process.

In a specific example of my new steel making process I charge an autoclave with 1000 kilos of sponge iron blooms ranging in size from about 30 to 80 mm. The autoclave is then evacuated. The autoclave while still under a vacuum is then charged with 2000 kilos of coal tar heated to a temparture of about 250 C. The autoclave is then heated at about 250 C. and the pressure builds up to about 8 kilos per square centimeter. These conditions are maintained for a period of about 2 hours. The excess of coal tar is then drained from the impregnated sponge iron. The latter is found to contain about 20 per cent of carbon uniformly distributed throughout its pores. An equal degree of impregnation can be attained by omitting the initial evacuation of the autoclave but continuing the heating for an additional hour. The impregnated sponge iron can be further heated if desired to drive on volatiles but the temperatures used should be sufficiently low to prevent any substantial carburization of the iron and loss of carbon.

The impregnated sponge iron obtained as above is employed in a steel making process in which tons of molten scrap iron from a mixer and 50 tons of impregnated sponge iron are charged into an open hearth furnace lined With silica bricks. This charge is converted in conventional fashion in contact with an acid slag. A steel is obtained which is of highest quality with extremely favorable mechanical characteristics.

While I have described what I consider to be the most advantageous embodiments of my process it is evident, of course, that various modifications can be made in the specific procedures which have been described Without departing from the purview of this invention. My impregnated sponge iron can be employed in any steel making process at any point of the process where the addition of carbon to the charge is required. Thus if the carbon content has been worked down below the required limit before the heat is ready for tapping it is possible to increase the carbon content of the charge by adding my impregnated sponge iron. This addition is more advantageous than pig iron since less is required owing to the higher carbon content of the sponge iron. It is also possible to add the impregnated sponged iron to the ladle for a final correction of the carbon content. While it is possible to entirely dispense with the use of pig iron in my steel making. process it is equally possible to employ pig iron in conjunction with my impregnated sponge iron. The relative costs of the two products will usually be determinative as to what proportions of these components are employed. But if it is desired to produce steel of the highest quality my sponge iron product should be used substantially as the sole carburizing component of the charge. Other modifications of my process which fall within the scope of the following claims will be immediately evident to those skilled in this art. For example, in the making of steel it is usually necessary to employ in the charge no more than from about 15 to a maximum of 50 parts of my impregnated sponge iron to 100 parts of scrap iron or steel.

What I claim is:

1. In the acid process of making steel in contact with an acid slag, the improvement which comprises charging a steel furnace with metallic steel-making ingredients and including in the charge, as at least a substantial part of the carburizing, deoxidizing degasifying component, blooms of sponge iron which have been impregnated substantially uniformly and to their deepest regions with from about 10 to 20 per cent of free carbon in a highly dispersed state by treating the blooms with an excess of a liquid hydrocarbon containing free carbon dispersed therein at temperatures ranging from about room temperature to 350 C., the temperature employed being high enough to render the hydrocarbon sufiiciently fluid to penetrate the pores of the sponge iron, followed by draining off the excess hydrocarbon material; and converting the charge in the furnace in contact with an acid slag to produce steel.

2. The process of claim 1 wherein the sponge iron blooms are from about 30 to mm. in diameter.

3. The process of claim 1 wherein the sponge iron blooms are subjected to a vacuum to remove air from their pores prior to completion of the impregnation step.

4. The process of claim 1 wherein the sponge iron blooms are subjected to a vacuum to remove air from their pores and then to superatmospheric pressures to drive the bituminous material into their pores prior to completion of theimpregnating step.

5. The process of claim 1 wherein the sponge iron blooms are impregnated by-heating them immersed in an excess of a liquid bituminous material for a period of from about 2 to 5 hours.

6. In the manufacture of steel by the acid open hearth process, the improvement which comprises charging an open hearth furnace with metallic steel-making ingredients and including in the charge as substantially the sole carburizing, deoxidizing-degasifying component sponge iron blooms impregnated with from about 10 to 20 per cent of free carbon by heating the blooms immersed in an excess of a liquid bituminous material for a period ranging from about 2 to 5 hours at a temperature not substantially exceeding 350 C. high enough to render the bituminous material sufficiently fluid to penetrate the pores of the sponge iron, followed by draining off the excess bituminous material; and converting the charge in the furnace to steel in contact with an acid slag.

JEAN CHARLES FOURMANOI'I.

6 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. IN THE ACID PROCESS OF MAKING STEEL IN CONTACT WITH AN ACID SLAG, THE IMPROVEMENT WHICH COMPRISES CHARGING A STEEL FURNACE WITH METALLIC STEEL-MAKING INGREDIENTS AND INCLUDING IN THE CHARGE, AS AT LEAST A SUBSTANTIAL PART OF THE CARBURIZING, DEOXIDIZING - DEGASIFYING COMPONENT BLOOMS OF SPONGE IRON WHICH HAVE BEEN IMPREGNATED SUBSTANTIALLY UNIFORMLY AND TO THEIR DEEPEST REGIONS WITH FROM ABOUT 10 TO 20 PER CENT OF FREE CARBON IN A HIGHLY DISPERSED STATE BY TREATING THE BLOOMS WITH AN EXCESS OF A LIQUID HYDROCARBON CONTAINING FREE CARBON DISPERSED THEREIN AT TEMPERATURES RANGING FROM ABOUT ROOM TEMPERATURE TO 350* C., THE TEMPERATURE EMPLOYED BEING HIGH ENOUGH TO RENDER THE HYDROCARBON SUFFICIENTLY FLUID TO PENETRATE THE PORES OF THE SPONGE IRON, FOLLOWED BY DRAINING OFF THE EXCESS HYDROCARBON MATERIAL; AND CONVERTING THE CHARGE IN THE FURNACE IN CONTACT WITH AN ACID SLAG TO PRODUCE STEEL. 